The present invention concerns hydrocarbon soluble alkyl lactone polyol esters, their method of preparation and the utility of said lactone polyol esters preferably in hydrocarbon fuel and lubricating systems as stable sludge dispersants and/or varnish inhibiting additives.
During the past decade, ashless sludge dispersants have become increasingly important, primarily in improving the performance of lubricants and gasoline in keeping the engine clean of deposits and permitting extended crankcase oil drain periods. One category of ashless dispersants involves the esterification product alkenyl substituted acids, e.g. polyisobutenyl succinic acids, with polyols e.g. pentaerythritol, as taught in U.S. Pat. No. 3,381,022; however, such a dispersant oftentimes contains unsaturation making it susceptible to oxidative degradation especially under high severity conditions such as elevated oil temperatures and extended drain intervals. The esterification of alkenyl halolactone acids with pentaerythritol as taught in U.S. Pat. No. 3,755,173 affords more hydroxyl groups per chain but the inherent propensity of such dispersants towards elimination of corrosive HCl to give unsaturated dispersants can promote decomposition of the hydrocarbon lubricant, corrode metal engine parts and promote varnish deposition on the internal surfaces of the engine.
Other lactone esters formed from alkenylsuccinic anhydride with a polyol with acid catalyst have been recently disclosed in U.S. Pat. No. 3,936,472. However, the mode of preparation and stoichiometry afforded high molecular weight, viscous products devoid of hydroxyl groups which are believed to be essential to sludge control.
The present invention overcomes all the shortcomings of the prior art by designing polyalkyl lactone polyol esters free of unsaturation and halogen, with enhanced stability and outstanding activity as varnish-inhibiting dispersants.